Hammer mill



T. C. ALFRED HAMMER MILL Filed July 17 2 Sheets-Sheet m m m T. C. ALFRED HAMMER M I LL Oct. 27-, 1931.

Filed July 17, 1928 2 Sheets-Sheet Gummy; I

Patented Oct. 27, 1931 THEoDonE c. ALFRED,

PATENT GFFlCE OF LANCASTER, OHIO HAMMm MILL Application filed July 17,

' This invention relates to improvements in hammer mills and has particular reference to hammer mills of the type including a casing which is mounted a rotor carrying a plu- 1 5rality of centrifugally acting hammers which, upon rotation, assume extended positions contacting with the material introduced into the casing so as to reduce such material to a divided comminuted form.

0 It is an outstanding object of the invention to provide a reduction or hammer mill of the type set forth wherein is provided a power driven rotor and a suction producing fan by means of which rotor the material acted upon and reduced by the rotor and its amociated hammers may be suitably screened and then by the action of the fan withdrawn from the ca ing of the mill and transmitted to a suitable point of discharge.

' It is another object of the invention to pro vide separate shafts for the rotor and thefan and to provide power transmitting means between said shafts so that both the rotor and the fan may be driven from a common source 5 of power and at proper relative rates of speed to secure the most eflicient operation. v

It is another object of the invention to construct the rotor and associated hammers so that the mill will be very eflicient from a standpoint of being able to grind or reduce the materials placed therein to a relatively fine form-of subdivision, to enable the mill to have a relatively large capacity in proportion to the size of the rotor and the general dimensions of the mill and at the same time to permit of the use of a prime motor having horse power equivalent to that commonly found in connection with power plants ac of farm tractors or larger power plants.

lVith these and other objects in View which will appear as the description proceeds, the invention consists in the novel features of construction, combination of elements and 14.5 arrangement of parts hereinafter fully dehed and pointed out in the appended ccompanying drawings: 1 e is a vertical longitudinal sectiontall- 11 through a hammeriui'll con- 1928; Serial No. 293,400.

structed in accordance with the present invention, I

F lgure 2 IS a plan View of the null withthe cover section of the casing removed,

Figure 3 is a vertical sectional view taken {2 reduction mill in its entirety. Broadly, the

mill comprises a casing'or housing which includes a heavy base section 2, embodying heavy cast metal side plates 3--3 and a transversely extended curved bottom plate 4, also of cast metal. The plates 33 are provided with ribs or flanges 5 constituting seats for the plate 4, and transverse section tie rods 6 passed through a line of openings formed in the outer edges of the plate 4; so as to firmly unitethe plates 33 with the bottom plate 4 and to produce a solid, rigid construction fully capable of withstanding the service and conditions to which a mill of this character is placed. In combination with the base section 2 the housing of the mill includes a cover or hinged hood section 7. This hood section is hinged as at 8 to the base section and includes spaced side plates 99, which register with the plates 3-3. Between the plates 99 there is secured a transversely extending arched wall 10, which is held between the plates 9--9 by means of the tie rods 11. In operation the base section of the housing and the cover section occupy the closed relationship as set forth in Figure 1 so that thereis produced within the housing a rotor chamber 12 in which material is fed and reduced to a subdivided form as will be apparent hereinafter.

" The plates 3-3 contiguous to their upper edges are provided with outstanding brackets 13, which constitute foundations for the reception of journal bearings 1 which receive for rotation a rotor shaft 15. One end of this shaft is provided with a belt wheel p or the like 16 by means of which the rotor shaft may be revolved by any suitable source of power, most oftenafarm tractor, although the device maybe equipped-with its own moftor. Arranged on the rotor shaft within the chamber 12 is a rotor 17. This rotor comprises-a plurality of discs'l8-, each-.disc being provided. with a :spacer 1.9 so that: uniform spaces will be provided between each pa r of'adjoining discs. Contiguous to their periin'eters the discs 18 are formed withregister- 'ing openings for the reception of transverse- 1y extending hammer shafts, or rods 21', and 1 rotatably mounted upon. these, shafts and adapted to occupy. the spaces 20 are a plurality of centrifugal. hammers; 22. Each, of

' these.hammers, as shown in Figure. 4-, comprises-a flat bar of; metal/stock having the ends thereof formed to includexstepped. or notched projections 23, and ad aicentrtoth'ese projections each hammer: is pitovided with an opening 2 L adapted for the receptionaoftl'ie particularl'shaft-orrod221. uponwhich the he hammer may be mounted. llnoperati'on'.

Whenthe rotor is revolved atworking'speeds,

"the hammers; as/shownv in. Figure 1,. corresponding to centrifugal forcesyassume an extended:radiali positi'on with respect tothe axis of. the rotor shaft so thatthe' outer ends of the hammers willclosely engagewith the Walls ofthe chamber 12 to contact or; strike the loose materialsrfe'd into the chamber and the velocity .of the rotor andv the action ofi the hammers, to reduce such material-to thedesired' stateof subdivision. Theehammere, it: will be observed, are 5 double endedso aha when one end: wears to too greatsian extent for: furt-hereffectiveuse; the hammer may. bereversed a)? present its 'other'e'nd and thereby: restore the" efiiciency of 1 the: device.

I prefer to use the double openings 2k-ratherthan an: elongated slot for; thefreason that such: openings; preserve toqbetter advantage the relationship betweenv theend of." each hammer andet-he' wall-l'of the chamber- 15.- 5-By reference to Figure 5 itiwillsbe observed'athat the hammersare set in substantially 'V shaped relationship aroundthe periphery of the retor.-. This-V shaped'arra-ngement of the ham 'mers. is of very great importance in: confine ing the-material. hez-re'ducedlto the-0011+ fihes of the v rotor proper: The -;ar ran gement permits the. material to. work 'toward't'heicen;

ter ;of ithe rotor where it is: boundito be struck bythe flying hammers; ln fact ith'e V'shaped arrangement provides a conveyor" actiony. pre

" 'I venting? the scattering of. 'the 'material to: in-

accessible corners ofllthez. rotorichambe'r or,

the I hammers were arrangeddn =Xxorder or: in 6 5 Worden; a

The hood section 7 provides a receiving mouth 25 into which the loose material such as fodder, hayand various grains may be-fed into the reduction chamber 12. To facilitate this there is :provided a serving table 26 which in operation assumes the incline position shown in Figure l and is retained in such position by supporting rods. 27.: The end of this table nearest the mouth 25 includes a pocket 28, whichacts as'a trap to minimize the possibility of foreignmaterials such as metals entering the rotor chamber with the feed materials to be. ground. Preferably, the inner surfaces .of the walllO are roughened or corrugated as at 29"to assist in'the material reduction' action of. the mill when. the rotor is revolvedi Y It will beobserved. that; the hammers do 110tt01l0ll any of j the metal parts-or wallsof thev rotor. chamber and contact merely-with the material under process of 'reduc- ,tion; This resultsin prolonged life on the part; of the. hammers withlbut minimum wear; V V

The intermediate portion of the housing,

around the "lower part: of. the rotor, is provided with a: removable perforated shell or plate 30. This plate acts as ascreen enabling material of proper fineness to sift through the same' intolthe fan; or, outlet chamber3l arranged; 'in'thezlower part of the housing. 1

The iplate' or screen 30 may. be. readily removed by lifting the-hoodsection 7-. This permits: screens havingvarious effective. sizes to be used in connection-with'the rotor.

l/Vithin the. outletlchamber 3'1v there is proadded a. longitudinally extending shaft 32,

"upon which aremounted-agitator blades 33.

. llhece:blades upon the-.rotatien'of the'shaft 32, serve to advance the finely ground mate; rial rece ved within theoutlet chamber, to ward' a fan chamber'3t; formed in connection I w-iththe. basesection- 2 andiarranged at one side thereof. The: fan chamber is produced by a housing35, secured to one of the plates 9 withinthe chamber 34,;to expel the samezfrom themaehineby wayof. an outlet duct 37 which leads to. a suitable point; of discharge. The outer endof the shaft 32 is provided with. a

belt wheel around which is trained a belt 38 which leads to a wheel 39 carried by one end 1 of the rotor shaft. idler 10 engages with the'belt 38' to maintain the rotor in the re quiredftaut condition suitable for the best operation. Entering the outlet chamber 81.;

below 'the screen 30 or to one" side of said screen, is an-air inlet conduitel which provides for better air circulation through the housingand facilitatesthe withdrawal of the ground material. The housing may also provided with supplemental air inletopenings -4l2, the5,opening r and closing of which maybe regulatedibyan adjustable slide 43.

In thedesign of thishammer mill careful u. Disposed within. saidchamber is a fan 38' which operates upon. the. material, received I attention has been given to various engineering factors which play such an important part in securing effective and eihcient operation. The width ofa rotor, for example, is

determined more or less by the size of the rotor shaft and the velocity or speed of the rotor by thestrength of the materials comprising the same or, in other words, the relation of the tensile strength to the centrifugal force developed. Theoretically, at least, the higher the rotor speed the more effective the reduction of materials handled thereby because of the increased velocity, which enables the hammers to deliver harder blows and to permit such hammers to pass a given point oftener, striking more blows per minute: Practically, of course, the speed is controlled by other factors, especially where the mills have the fan mounted directly on the rotor shaft. In the present invention it will be noted that the fan is mounted on its own shaft independently of the rotor shaft. At excessive speed it takes a considerable amount of power to drive the fan and because of the very nature of the work done by the mill, which consists of a series of shocks, the speed must be less than would be safe for a fly wheel of the same material. that simply revolved and had no other work to do.

Tests have disclosed that 3000 R. P. M. is the most eflicient speed for a 22 inch diameter rotor, although this is approximate and. such mills may run faster or slower. Naturally, the diameter of the rotor must be taken into consideration, as the peripheral speed of the rotor, regardless of size, should be about the same. It is quite possible to manufacture a mill with avery small rotor to operate at a speed of 7000 HP. M., and again going to the other extreme, it is possible to operate satisfactorily a larger rotor at a speed of 700 R. P. M. or less.

With a small diameter rotor a-higher speed is necessary to obtain the desired peripheral speed and to produce the necessary forces for shattering material because there is practically no weight comparatively to the rotor itself. The chief drawback of the small rotor is that the spread between the bearings, that is side walls of the housing, cannot be great. In fact, about six inches is very nearthe limit for a small machine which, as a consequence, possesses little or no utility for handling farm products, such as car corn. The small high speed mill has one outstanding advantage and that is, more hammers will pass a given point in a given length of time which, of course, means a finer product. However. to widen the space between the bearings on the small cylinder suiiiciently to take in the average grinding commodity would mean instant breakage of the mill. As a consequence the-rotor shaft has to be madelarger in order to stand a greater hearing spread, also the discs must be larger, and

as a consequence, the speed must be reduced so that the larger the mill the slower it must operate and as a consequence f wer hammers will pass a. given point in a definite length of time.

From apower standpoint, a four pin rotor using three discs and a hammer on each pin between the discs, or a total of eight hammers staggered slightly, would require eight horsepower to operate the same to cover an area on the screen of approximately two inches in width and, in this connection, each additional set of four hammers would re quire four more horsepower and so on. It is known that a six pin rotor, travelling at the same speed as a four pin rotor, and carrying a full set of hammers on each pin, will strike fifty per cent more blows at any speed than the four pin rotor. Also an eight pin rotor will strike twice as many blows at the same speed as the four pin rotor, and this could be carried on indefinitely. The drawback here is, however, that it would take about one horsepower per hammer to satisfactorily operate such mill at efficient grinding capacities. This is because of the resistance of the hammer itself on the incoming material and hammers cannot be added at will without materially increasing the horsepower requirements of the machine. Furthermore, the arrangement of the hammers on the rotor has considerable to do with the power requirements. The standard or more common way of mounting the hammers on the disc pinsis to situate a series or a battery of hai mers upon each pin. A rotor having lOdiscs would have nine spaces between the discs and a four pin battery assembly would then require 36 hammers. This would cover an area, depending upon the design, of approximately 15 inches. hen a hammer mill is large enough to accommodate the materials to be ground, such as roughage, ear corn, fodder and the like grown on farms, a standard condition is reached. To make the mill still larger it is necessary to add additional. harnmers to cover the greater screen width and this would require additional horsepower. Since the average farm power is in the form of a tractor developing about 20 to 25 horsepower, a limitation is placed onthe size of the hammer mill, since the rotor must be made to function with the power generally available on a farm. For example, a reduction mill requiring at least 40 horsepower to operate efficiently, would not find wlde favor for the reason that its power requlrements are too high and are not available to the ordinary farmer. It would be much better to operate two small units of lower horsepower than one large unit, for two reasons: The large unit would necessarily have a much heavier shaft, and as aconscquence larger discs. which would make it operate at slower speed and additional hammers would have to. be hadjto cover the additionalscreeniwidth,

but becauseof the larger diameter-of the-ro.+ tor, ;less-"hamm'er's would pass a givenrpoint in the same: length of time, as the speedof this mer'blows, additionalpins would have to be This. could.

unit could not be much over 2200 R. P3 M.,

consequently to-get the same number of hamadded to carry morehammers. lee-worked out. satisfactorily but the result would be power requirements far in excess/f "that which is ordinarily available;

" On av reduction: mill of any size theefh ciency should be'the same when adding any number ofunits of the same dimensions. In

' otherwords, a inch mill with 36 hammers requiring -horsepower, and a 30 inch mill of the same dimensions would require 80' horsepower, and a- 4-5 inch mill- 120 horsepower. Thedifliculty is that structural objects are encounteredin attempting to widen than necessary to accommodate the materials to be ground,

Now it is quite evident that a15. inch mill meetstherequirements so far as accommodatingmateriall1s concerned. If this were made inbattery type assembly, using four pins, 36'

hammers would bereq uircd to properlyco ver the screen. Therefore, it isquite evident that 'ifsome' arrangement of hammers could be devised. that would elfectivelycover this, same area with a smallernumber of hammers, less horsepower would be required. Theprod'uct,

- of course,.will-noti be as finely'ground at. the

same speed, but commercially the limitation is-more from, the-power'to be-appliechas the product of fewer hammers isquite satisfactory',.and ifit is possible. to mainta n in the mill a flexibility of hammenapplicat on so i that: additional hammers can be. applied as additional power isavailable aJvery 'desir'- able situation: or combination is efiected, This is secnredlby thedlmensions of the rotor disclosed herein with; the substantial V, ar-

rangem'en t of the hammersas setfforth. in Figure l 7 1 Tests'h ave been made with. thisV type'of rotor,using' IG'ham'mers with thinner discs ouerthesame screenaremnamely 15 inches,

but-ithhas'been found that: suchxa' mill is reallyutoo great aload for an ordinary farm tractor landii-n the-designof thefpr'esent inrehtion, my problem was to main'tainihe 15, inchfmillfand-still cover the screen ifpossible with fewer hammers. This-I accomplished by making the discs 1.8,thicker,ino'therrwords using, fdiscshaving a thickness j of one-half aninchwhere before one-qu'arterinch discs wereused, andr-educ ng the. number of hammers to 12.

V Generallyspeaking, I consider the mill to require eight horsepower when running empty, which leaves. '12 horsepower the.. 1iormal; 2.0; available for; grinding, orv

one horsepower per hammer, givingt-he' desired arrangement. when thetmill is oper ated with farm tractorapower. Y r

Furthermore, in increasingthe thickness of the discsijonithe rotor, Lhave added weight to the. revolving part of the' mill and this produces a, flywheel :a'ction, which-gives more uniform application of the power and eliminates to a great extent the jars and jerks found on mills .wherethis unit islighter in weight. V

As shown in Figure 5 the hammers 22 are arranged in a V order about the rotor, there being two hammers to a pin on: a, siX pin rotor. This is an eflicient number of hammersfor the production of a satisfactorily ground product, and. conforms to the, light power availableonanaverage farm. The V arrangement of the hammers has a tendency to throw the material back and forthwithin the. upper housing, while with an aligned or battery arrangement of hammers,- the material simply follows around inthei direction of the rotor The six pinsare used so that there will not; be too great aspace between the ham mers around the circle, as a type...g,rrangement would not be desirable on a four pin rotor. It wlouldbe satisfactoryon an eight pin rotor, but this Would require 16 hammers which places too great a load on the power supplying unit, 7

. To make the rotorlarger'would' mean less speed, reducing the number of hammer blows, 1

an dito make it. smaller would require a greater: speed, and whlle this would improve the cfiiciency or the mill "its capacity to receive materialsuita-ble for farm usage is obstructed.

With these featuresinlniind, I have constructed the present, invention so that the rotor'includes-siX pins with'two hammers on each pin, 'whi ch provides approximately one horsepower per hammer -whenqa Fordson tractor is used. When a 25 horsep'ower'operating' motor, i'sused, it simply means that the machine will handle a little largerfquantity, although the sample willbe' somewhat coarser because ,there is being fed more material against a definite number of hammer blows per minute. However, when 30. horsepower is applied to the rotorshaft, thereis added another set of12 hammers to'the rotor in a double V or X formation. This is maintained uptoeO horsepower." When 50 horsepower is used I put on 36 hammers, in staggered formation, since this flexibility of hammer application is v eryxde' imbl f I Thisgives a wide spread of usage or adapt ability forthe mill, and makes it"p'o'ssible forone size mill to fit ,in where ordinarily'it reou res three sizes. In. the battery type of mill there c'an be added a certain amount of: -a dd1tional horsepower, for example 10",. to-

advantage, but to continue toaddhorse'power tothe 'millland to feed itmorelheavily, will is not satisfactory, and, of course, in the battery type of four pin rotor there is no room for additional hammers, so that the range is limited, and as a rule specifications on a mill of this kind will be given with a 10 horsepower spread, while in the present invention a flexibility of hammer assembly enables the mill to be rated from between 15 to 50 horsepower.

In View of the foregoing it will be seen that the present invention provides a hammer or reduction mill wherein an improved rotor construction is provided by means of which the mill is rendered adaptable to the power equipment of ordinary farms, in that it is possible to use, without employing a special motor, a construction which will enable all sizes of farm products to be handled and reduced adequately to a proper form of subdivision. In this respect I have provided a hammer mill of large capacity with minimum power requirements. It will be understood that as additional power is available more of the hammers may be added to the rotor. This enables the mill to possess a greater capacity without material change in its construction. In fact, the mill can operate efiiciently when power to the extent of 15 to 50 horsepower is being applied thereto.

What is claimed is:

In a hammer mill, a casing, a reduction rotor mounted for rotation in said casing, a semi-cylindrical screen in said casing below said rotor, said screen serving to divide the interior of said casing into a rotor chamber and a discharge chamber, said casing being formed to include an opening parallel with and adjacent one horizontal edge of said screen, adjustable means for efiecting the closure of said opening and a conduit connected with said casing below said opening for admitting air into said discharge chamber.

In testimony whereof I aflix my signature.

THEODORE O. ALFRED. 

